Phosphor Composition

ABSTRACT

A method is disclosed for forming a blended phosphor composition. The method includes the steps of firing precursor compositions that include europium and nitrides of at least calcium, strontium and aluminum, in a refractory metal crucible and in the presence of a gas that precludes the formation of nitride compositions between the nitride starting materials and the refractory metal that forms the crucible. The resulting compositions can include phosphors that convert frequencies in the blue portion of the visible spectrum into frequencies in the red portion of the visible spectrum.

RELATED APPLICATION

The present patent document is a division of U.S. patent applicationSer. No. 12/271,945, which was filed on Nov. 17, 2008, and is herebyincorporated by reference in its entirety.

BACKGROUND

The present application relates to phosphors. In particular, theapplication relates to nitride phosphors that can convert blue photonsfrom a light emitting diode into frequencies within the red portion ofthe visible spectrum. The production of such red tones helps tailor thecolor produced by an LED lamp, and in particular red photons helpproduce warmer white light from LED lamps.

Lighting is done in a number of different fashions. Incandescentlighting uses the emission from a tungsten filament to produce thecharacteristic light. Fluorescent lighting uses an ultraviolet source(mercury emission) to strike a photoluminescent material that producesthe white light emission from a fluorescent lamp. Halogen lighting alsouses a tungsten filament but includes a trace of halogen gas (typicallyiodine or bromine) that helps regenerate the tungsten filament duringoperation which in turn increases the lifetime of the lamp. Solid statelamps emit photons when a current is directed across a p-n junction (orits equivalent).

Each of the relevant forms of lighting have corresponding advantages anddisadvantages. Incandescent lighting typically produces warmer colorsand bulbs and fixtures are widely available at low cost. From an energyefficiency standpoint, however, incandescent bulbs tend to produce mostof their energy as heat rather than light. Indeed, future regulatoryschemes may minimize the availability of the most common incandescentbulbs.

Fluorescent lighting tends to be more energy-efficient that incandescentlighting, but requires starter circuits and related hardware. As aresult, cost-effective fluorescent lighting that can be used inincandescent fixtures has only recently been developed. Fluorescentbulbs also typically contain mercury, even though in minimal amounts.Solid state lighting has the advantage of long lifetime, higher energyefficiency and potentially lower cost, but has historically sufferedfrom low brightness and (as indicated elsewhere) the unavailability ofthe relevant colors that can produce white light.

More recently, solid-state lighting has become commercially availablebased on the increased availability at competitive prices of lamps basedon light emitting diodes that can produce white light. Althoughsolid-state devices (light emitting diodes) have been used for indicatorpurposes for several decades, two factors limited or precluded the useof light emitting diodes as the basis for illumination: the lack ofdiodes that could produce the frequencies required to produce whitelight; and, once such diodes became available, their generally lowbrightness.

Advances in the art have reduced these (and other) barriers to solidstate lighting. First, blue light emitting diodes have been available atcompetitive prices in commercial quantities for over a decade. The bluelight emitting diode is a necessary component of white light because (asexplained below) the blue photons are required either to contribute to athree color lamp or to excite an appropriate phosphor.

As a second advance, the brightness of available LED lamps continues toincrease.

Because white light is a combination of many frequencies within thevisible spectrum, it can be produced from blue, green and red primarysources. Thus, a lamp that emits white light can be produced from one ormore red light emitting diodes, one or more green light emitting diodesand one or more blue light emitting diodes. This technique can berelatively complex, however, because of the number of diodes required.

In the recent growth of white light-emitting lamps using light emittingdiode sources, the most common method has been to incorporate a lightemitting diode that emits in the blue, violet or ultraviolet portions ofthe electromagnetic spectrum. Such a diode is then combined, usually ina package that includes a lens, with a phosphor that absorbs the blue(violet, UV) emission and produces a yellow emission in response. Thecombination of the blue light from the diode and the yellow light fromthe phosphor gives white light.

As well-understood in this art, a phosphor is a composition thatgenerally absorbs a given frequency, or range of frequencies, of lightand then emits different color photons, usually of a lower frequency andusually including a range of frequencies.

A typical phosphor is a solid composition that includes an (activator)ion in a host structure. Because light emitting diodes that will produceblue light are relatively new in commercial appearance (about a decade),the use of blue light emitting diodes combined with yellow phosphors toproduce white light is also relatively recent.

Different white light sources, however, have slightly differentappearances to the human eye. These are sometimes quantified using awell-recognized measurement referred to as color temperature. Whenstated descriptively, white light that is more bluish in tint isreferred to as being cooler, while light that has more of a yellow orred component is generally referred to as being warmer. Depending uponthe desired end use, cooler lamps are preferred in some circumstanceswhile warmer whites are preferred in other circumstances. As oneexample, skin colors tend to look more natural under warmer lamps thanunder cooler ones.

In general, incandescent lighting is warmer than fluorescent lighting;although warmer fluorescent lamps are available. In any case, if LEDlighting is to successfully replace incandescent and fluorescentlighting (for reasons in addition to its energy advantages), diode lampsthat will emit with a red or yellow component to give a warmerappearance will be desired.

Because blue light emitting diodes are relatively recent, the need orcommercial desire for phosphors that can convert a blue photon into ared emission in the context of an LED lamp is also relatively recent.One predominant source for such a phosphor is set forth in internationalapplication number WO2005052087 (and also published as US20070007494).This publication describes a nitride-based phosphor that is relativelyrecent in its commercial appearance. The phosphor composition is formedof materials that are highly reactive in water or air, and thus isrelatively difficult to produce without sophisticated equipment.

In most typical LED applications, a phosphor must have color stability;i.e., its chemical composition must be consistent enough over the courseof time so that the color of the light emitted by the lamp remainsconsistent. Stated differently, if the phosphor chemical compositionbreaks down relatively quickly, the color produced by the diode lampwill change quickly, and usually in an undesired manner.

The phosphor described in the '087 publication is also expensive,available only from limited sources, and because of manufacturingdifficulty, is sometimes hard to obtain. For example, the siliconnitride that is typically one of the starting materials is relativelyinert, even at high temperatures. Indeed, because of itshigh-temperature stability, silicon nitride is typically used aspassivation for semiconductor components. Additionally, the alkalineearth metals that represent other starting materials react quickly(often too quickly) with oxygen and moisture.

Accordingly, a need exists for improved processes and resulting phosphorcompositions that will produce a red emission, when stimulated by a bluephoton that are stable in their composition and color output, and thatare more easily manufactured than currently available phosphors havingthis characteristic.

SUMMARY

In one aspect, the invention is a method of making a phosphorcomposition that down-converts photons in the blue and ultravioletportions of the visible spectrum into photons in the longer wavelengthportions of the visible spectrum. The method comprises mixing acomposition containing a cation from the group consisting of calcium,strontium, lithium, sodium, potassium, rubidium, cesium, magnesium,barium, scandium, yttrium, lanthanum, gadolinium, and lutetium with acomposition containing a cation from the group consisting of aluminum,silicon, boron, gallium, carbon, germanium, and phosphorus, and with ananion selected from the group consisting of nitrogen, sulfur, chlorine,bromine, and iodine. The compositions are also mixed with an activatorselected from the group consisting of europium (II), cerium (III),ytterbium (II), samarium (II) and manganese (II). The mixture is heatedin the presence of a forming gas at or near atmospheric pressure and ina refractory crucible that is substantially inert in the presence of theforming gas mixture. The temperature is sufficient to produce thephosphor but less than the temperature at which the precursorcompositions or the phosphor would decompose or react with the crucibleand the reaction is carried out for a time sufficient to produce aphosphor that down converts photons from the ultraviolet and blueportions of the visible spectrum into photons in longer wavelengthsportions of the visible spectrum.

In another aspect, the invention is a method of making a phosphorcomposition that comprises mixing a nitride selected from the groupconsisting of nitrides of calcium and nitrides of strontium with anitride selected from the group consisting of nitrides of aluminum andnitrides of silicon with a europium source composition in thesubstantial absence of water and oxygen. The mixture is heated in thepresence of a forming gas that is a mixture of hydrogen and nitrogen atabout atmospheric pressure, and in a refractory crucible that issubstantially inert in the presence of the forming gas mixture. Thetemperature is sufficient to produce the phosphor but less than atemperature at which the precursor compositions or the phosphor woulddecompose or react with the crucible and the reaction is carried out fora time sufficient to produce a phosphor composition that will downconvert photons in the blue and ultraviolet regions of the spectrum intophoton in the longer-wavelength regions of the visible spectrum.

In another aspect, the invention is a method of making a phosphorcomposition that absorbs in the blue portion of the visible spectrum andemits in the red portion of the visible spectrum. The method includesthe steps of mixing nitrides of calcium, nitrides of strontium, nitridesof aluminum and nitrides of silicon with europium fluoride in thesubstantial absence of water and oxygen, heating the mixture in thepresence of a forming gas that is a mixture of about 5% hydrogen and 95%nitrogen, at about atmospheric pressure, in a refractory crucible thatis substantially inert in the presence of the forming gas mixture, at atemperature sufficient to produce the phosphor but less than atemperature at which the precursor compositions or the phosphor woulddecompose or significantly react with the crucible, for a timesufficient to produce a phosphor composition with a nominal compositionof Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ mixed with an amount of silicon aluminumoxynitride of at least 1%.

In another aspect, the invention comprises firing precursor compositionsthat include europium and nitrides of at least calcium, strontium andaluminum, in a refractory metal crucible and in the presence of a gasthat precludes the formation of nitride compositions between the nitridestarting materials and the refractory metal that forms to crucible.

In another aspect, the invention is a phosphor composition that convertsfrequencies in the blue portion of the visible spectrum into frequenciesin the red portion of the visible spectrum. The phosphor compositioncomprises Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ (preferably where 0<x<1 and0<y<1) combined with silicon aluminum oxynitride in an amount of atleast 1% by weight.

The foregoing and other objects and advantages of the invention and themanner in which the same are accomplished will become clearer based onthe followed detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of relative intensity of phosphor emission plottedagainst the wavelength in nanometers (nm) for phosphor compositionsaccording to the present invention.

FIG. 2 plots the variability of the relative brightness (top) and therelative color (bottom) of the emission against the atomic fraction ofstrontium in phosphors according to the present invention

FIGS. 3 and 4 are plots illustrating variations in brightness and colorfor commercial phosphors and phosphors according to the presentinvention.

FIG. 5 is a top perspective view of the interior of a reaction vesselaccording to the present invention.

FIG. 6 is a perspective view of the reaction arrangement according tothe present invention.

FIG. 7 is a cross-sectional view of the reaction vessel illustrated inFIGS. 5 and 6.

FIG. 8 is an x-ray powder diffraction plot for a phosphor compositionaccording to the present invention.

DETAILED DESCRIPTION

In a broad aspect, the invention is a method of making a phosphorcomposition that down-converts photons into the longer wavelengthportions of the visible spectrum. The method comprises mixing acomposition containing a cation from the group consisting of calcium,strontium, lithium, sodium, potassium, rubidium, cesium, magnesium,barium, scandium, yttrium, lanthanum, gadolinium, and lutetium with acomposition containing a cation from the group consisting of aluminum,silicon, boron, gallium, carbon, germanium, and phosphorus, and with ananion selected from the group consisting of nitrogen, sulfur, chlorine,bromine, and iodine.

As used herein, the phrase “composition containing a cation” refers to acomposition that will, under the reaction conditions, produce theelement as a cation in the resulting phosphor composition. The elementdoes not necessarily need to be present as a cation in the sourcematerial.

The compositions are also mixed with an activator selected from thegroup consisting of europium (II), cerium (III), ytterbium (II),samarium (II) and manganese (II). As in the case of the cations, theactivator can be added in the form of any composition that produces thedesired activator atom (typically as an ion) in the crystal lattice ofthe resulting phosphor and without otherwise interfering in an undesiredmanner with the process steps or the other starting compositions.

The mixture is heated in the presence of a forming gas and (in mostembodiments) in the substantial absence of water and oxygen at aboutatmospheric pressure and in a refractory crucible. In most embodiments,the crucible is substantially inert in the presence of the forming gasmixture. The temperature is sufficient to produce the phosphor but lessthan the temperature at which the precursor compositions or the phosphorwould decompose or react with the crucible and the reaction is carriedout for a time sufficient to produce a phosphor that down convertsphotons from the ultraviolet and blue portions of the visible spectruminto photons in longer wavelengths portions of the visible spectrum.

In another aspect, the invention is a method of making a nitridephosphor composition that comprises mixing a nitride selected from thegroup consisting of nitrides of calcium and nitrides of strontium with anitride selected from the group consisting of nitrides of aluminum andnitrides of silicon with a europium source composition in thesubstantial absence of water and oxygen.

The term “nitride phosphor” is used herein to describe phosphors forwhich the cation is predominately nitride and in which the amount of anyoxygen present in the crystal structure is so minimal as to avoidchanging the crystal structure from that fundamentally formed by thenitride. Stated in another fashion, the phosphors described herein arenot “oxynitride” phosphors.

Persons skilled in this art recognize that there is no bright line thatdefines the amount of oxygen present that causes the composition to becategorized as an oxynitride rather than a nitride, but generallyspeaking in a nitride phosphor, only very small amounts of oxygen arepresent.

As used herein, the phrase “europium source composition” refers to acomposition that will produce europium as the activator cation in thecrystal lattice of the phosphor under the reaction conditions set forthherein. As set forth elsewhere herein, europium fluoride is exemplary.

The mixture is heated in the presence of a forming gas that is a mixtureof hydrogen and nitrogen at about atmospheric pressure, and in arefractory crucible that is substantially inert in the presence of theforming gas mixture. The temperature is sufficient to produce thephosphor but less than a temperature at which the precursor compositionsor the phosphor would decompose or react with the crucible and thereaction is carried out for a time sufficient to produce a phosphorcomposition that will down convert photons in the blue and ultravioletregions of the spectrum into photons in the longer-wavelength regions ofthe visible spectrum.

In an exemplary aspect, the invention is a method of making a phosphorcomposition that absorbs in the blue portion of the visible spectrum(i.e., between about 430 and 480 nm) and emits in or towards the redportion of the visible spectrum (i.e., between about 530 and 750 nm).Persons skilled in this art recognize, of course, that the boundariesfor colors in the visible spectrum are used descriptively rather than ina limiting sense.

All of the techniques described herein with respect to the synthesis ofthe composition and of the measurement of its properties (e.g., x-raypowder diffraction), are generally well understood in this art and canbe conducted by persons of ordinary skill in this art without undueexperimentation. Accordingly, such well-understood techniques have notbeen otherwise described in redundant detail.

In this embodiment, the method comprises mixing nitrides of calcium,nitrides of strontium, nitrides of aluminum, and nitrides of siliconwith europium fluoride in the substantial absence of water and oxygen.This mixture is heated in the presence of a forming gas. The heatingstep is carried out in a refractory crucible (typically metal) that isdescribed in more detail in connection with FIGS. 5-7 and that issubstantially inert in the presence of the forming gas. The heating stepis carried out a temperature high enough to produce the composition at areasonable rate but less than a temperature at which the precursors orproduct compositions would decompose or at which the compositions andthe crucible would significantly react with each other.

Most typically, the heating step is carried out at a temperature ofbetween about 1500° C. and 1800° C. for a time sufficient to produce aphosphor composition with a nominal composition ofCa_(1-x-y)Sr_(x)Eu_(y)AlSiN₃ mixed with an amount of silicon aluminumoxynitride (typically Si₂Al₄O₄N₄) of at least 1% by weight. In typicalembodiments, x is between about 0.5 and 0.7 and y is between about 0.013and 0.017.

Under these conditions, the phosphor can be synthesized at or nearambient (i.e., atmospheric) pressures, thus offering significant processadvantages by avoiding the need for high pressure techniques andequipment.

In the methods according to the invention, the phrase “at or nearatmospheric pressure” is not intended to limit the reaction to exactlyone atmosphere of gas pressure, but instead is intended to describe areaction scheme in which high pressure (or any pressurized orpressurizing) equipment is unnecessary. Although the method of theinvention can be carried out at atmospheric pressure, it is not limitedto atmospheric pressure. Thus, the reaction can be carried out at moreelevated pressures if desired. In many circumstances, however, thecapability to produce the phosphor at atmospheric pressure isadvantageous because it simplifies both the process steps and thenecessary equipment.

The term “forming gas” is used in its well-understood meaning; i.e., amixture of nitrogen and hydrogen that is used in a variety ofapplications where the presence of hydrogen is advantageous, and inwhich the presence of the nitrogen favorably reduces or eliminates thepossibility of combustion. Forming gas usually has a high nitrogencontent and a small hydrogen content, with amounts of between about 5and 10% hydrogen being typical. In many circumstances, a mixture of 95%nitrogen and 5% hydrogen is commercially available and thus advantageousfrom a practical standpoint.

Although applicants do not wish to be bound by any particular theory, ithas been observed to date that under the present reaction conditions,pure nitrogen (i.e., 99.9% purity or above) does not form a suitablenitride phosphor. The forming gas also helps keep the europium in the(II) oxidation state rather than the (III) oxidation state. The forminggas also helps keep nitrogen from reacting with the crucible in a mannerdirectly analogous to oxidation. Under these conditions, and althoughthe applicants do not wish to be bound by any theory, the resulting 1%of silicon aluminum oxynitride may be gettering most or all of anyoxygen present in the starting materials.

In another aspect, the invention comprises the phosphor compositionformed according to the method.

In an exemplary embodiment, the calcium nitride starting material istypically (Ca₃N₂), the strontium nitride is typically (Sr₂N), thealuminum nitride is stoichiometric (AlN), and the silicon nitride isalso typically stoichiometric (Si₃N₄).

The refractory crucible is substantially inert in the presence of theforming gas mixture. Those skilled in the art will recognize thatsynthesizing a phosphor in an inappropriate or less suitable cruciblematerial can reduce the optical performance of a phosphor. Suchdegradation usual results from some reaction between the cruciblematerial and the reactants. For example, when aluminum oxide crucibleswere used in reactions similar to those described herein, the oxygenfrom the crucible tended to be incorporated into the resulting phosphorpowder which in turn demonstrated poor luminescent qualities. The use offorming gas with boron nitride crucibles tends to produce a dimmerresult than in the preferred embodiments.

In the present invention, crucibles of tungsten (W) and molybdenum (Mo)have been determined to be advantageous. Tungsten and molybdenum arerefractory metals, they can withstand high temperatures and are inertunder the correct atmospheres. In contrast to the method tungsten andmolybdenum are not stable in the '494 firing conditions described in the'494 publication (100% nitrogen) because they each form nitrides; i.e.tungsten nitride and molybdenum nitride respectively.

In the present invention, the firing atmosphere is a blend of nitrogenand hydrogen, typically 95% nitrogen and 5% hydrogen. The presence ofhydrogen helps prevent the formation of undesired tungsten nitrides andmolybdenum nitrides.

The heating steps (firing) can be carried out in several steps atdifferent temperatures with appropriate ramping in between. Thecomposition according to the present invention has been successfullyproduced using a one hour heating step at 800° C., followed by anotherone hour heating step at 1200° C. and a two-hour heating step above1600° C. (typically 1675° C.) with ramping steps of about 350° C. perhour between heating steps. A comparable phosphor has also been producedby heating the materials directly to temperatures above 1600° C.

Using the invention, yields have been observed in the 90% range and oninformation and belief at least 95% in most circumstances.

The resulting composition includes europium in a mole fraction (“y”) ofbetween about 0.013 and 0.017 and a mole fraction of strontium (“x”) ofbetween about 0.5 and 0.65. Thus, calcium is typically present in a molefraction of between about 0.333 and 0.487.

The method could also be used to produce a phosphor of the formulaSr₂Si₅N₈.

FIG. 1 is a plot of relative intensity versus wavelength for phosphorcompositions according to the claimed invention. The emission colors setforth in the figures are described mathematically using colorcoordinates based upon the 1931 CIE chromaticity diagram and that areabbreviated as ccx and ccy. Thus, the plots represent the ccy value ofdiodes incorporating phosphors according to the invention using bluelight with the ccx coordinate held constant at 0.290. In FIGS. 1-4 thephosphor was irradiated at a wavelength of between about 450 and 470nanometers (e.g., 454 nm) and the emission was measured on aconventional spectrometer (e.g., Instrument Systems Optische MesstechnikGmbH, Munich, Germany).

As FIG. 1 indicates, in the absence of strontium, the peak outputwavelength tends to be about 660 nm and the addition of increasingamounts of strontium produce a peak output increasingly similar to thatof commercial red phosphor such as that described in the '494publication.

The term “peak wavelength” is used herein in its conventional sense;i.e., the wavelength at which the optical power of a source (here thediode) is at a maximum. Most diodes emit a range of frequencies near thepeak wavelength, and thus in some circumstances the color of the diodeis expressed as the width at half maximum as a way of informing theskilled person about the characteristics of the emitted light.

FIG. 2 represent charts of relative brightness and color coordinatesversus the amount of strontium for compositions according to the claimedinvention. As the top portion (brightness) of FIG. 2 indicates, the bestresults were obtained at an atomic fraction of strontium of betweenabout 0.55 and 0.67. The bottom portion of FIG. 2 shows that the colorwas most consistent at an atomic fraction of strontium of between about0.58 and 0.67.

FIGS. 3 and 4 illustrate variation in brightness and color in bar chartfashion for commercial red phosphor and for phosphors according to thepresent invention. FIG. 3 shows the variation in brightness while FIG. 4shows the ccy achieved when ccx=0.290 for commercial red phosphor andphosphors with different amounts of strontium and formed according tothe present invention.

FIGS. 5, 6 and 7 illustrate additional aspects of the invention. FIG. 5is a top perspective view of a relatively large alumina crucible broadlydesignated at 10. In the method of the invention, the nitrides ofcalcium, strontium, aluminum, and silicon are mixed (typically aspowders) with the europium fluoride in a glove box (not shown), which isessentially free of water and oxygen. The powders are then loaded intothe tungsten or molybdenum crucible shown as the circular crucible 11resting on the floor 12 of the large alumina crucible 10. A gas flowtube 13 projects into the interior of the crucible 10 through thecylindrical wall 14.

FIG. 6 shows the crucible 10 and a lid 15 and the external portion ofthe gas tube 16. The alumina crucible 10 is placed in a box furnacebroadly designated at 17. The alumina crucible 10 is not absolutelyrequired. If the furnace itself is fitted to contain the forming gasatmosphere, the alumina crucible 10 illustrated in the drawings can beoptional.

The tube 16 is typically formed of a ceramic material, which is likewiseselected to be unaffected by the forming gas or by any of thecompositions used to form the phosphor or by the phosphor itself.

The box furnace 17 is then used to heat the materials using the thermalcycle described earlier.

FIG. 7 is a cross-sectional view of the alumina crucible 10 illustratingthe cylindrical wall 14 and the lid 15. The ceramic tube 16, 13 extendsthrough the wall 14 to the interior of the alumina crucible 10 and thearrows schematically illustrate the forming gas flowing over thetungsten or molybdenum crucible 11.

The resulting composition can be a formula that is stoichiometric or itcan include the silicon oxynitride as a separate composition or thesilicon oxynitride can be combined with the europium-based phosphor.Applicants do not wish to be bound by any particular theory and theexact molecular composition of the phosphor remains partiallyundetermined, subject to the information provided herein.

The mixture is pulverized in conventional fashion for use as may bedesired or necessary. The size of the pulverized particles depends onthe end application and in most circumstances can be chosen by the enduser.

FIG. 8 is an x-ray powder diffraction pattern of a phosphor compositionaccording to the present invention. The powder diffraction was carriedout in a conventional manner (Kα line of Cu, scanned from 10-60 degrees(2θ)) and the results are generally well understood by those of ordinaryskill in this art. These results can also be reproduced without undueexperimentation.

In FIG. 8, the solid circles represents diffraction peaks generated bythe phosphor, the open squares represent peaks generated by the siliconaluminum oxynitride, the open triangles represent the presence ofaluminum nitride, and one peak represents an unknown (to date) material.

Most importantly, FIG. 8 illustrates the presence of the siliconaluminum oxynitride phase. For comparison purposes, the x-raydiffraction patterns of various compositions are indexed under the JCPDSfile system (Joint Committee on Powder Diffraction Standards) forcategorizing x-ray diffraction patterns.

In the drawings and specification there has been set forth a preferredembodiment of the invention, and although specific terms have beenemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being defined inthe claims.

1. A phosphor composition comprising: Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃,where 0<x<1 and 0<y<1; and silicon oxynitride in an amount of at least1% by weight.
 2. The phosphor composition of claim 1, wherein thesilicon oxynitride comprises silicon aluminum oxynitride.
 3. Thephosphor composition of claim 2, wherein the silicon aluminum oxynitridecomprises Si₂Al₄O₄N₄.
 4. The phosphor composition of claim 1, wherein xis between 0.50 and 0.70.
 5. The phosphor composition of claim 4,wherein x is between about 0.55 and 0.67.
 6. The phosphor composition ofclaim 1, wherein y is between about 0.013 and 0.017.
 7. The phosphorcomposition of claim 1, further comprising aluminum nitride.
 8. Thephosphor composition of claim 1 that absorbs frequencies of betweenabout 430 and 480 nanometers and emits peak frequencies of between about530 and 750 nanometers.
 9. A phosphor composition comprising: a firstphase comprising Ca_(1-x-y)Sr_(x)Eu_(y)AlSiN₃, where 0<x<1 and 0<y<1;and a second phase comprising silicon aluminum oxynitride.
 10. Thephosphor composition of claim 9, wherein the silicon aluminum oxynitridecomprises Si₂Al₄O₄N₄.
 11. The phosphor composition of claim 9, whereinthe silicon aluminum oxynitride is present in an amount of at least 1%by weight.
 12. The phosphor composition of claim 9, further comprising athird phase comprising aluminum nitride.
 13. The phosphor composition ofclaim 9, wherein x is between 0.50 and 0.70.
 14. The phosphorcomposition of claim 13, wherein x is between about 0.55 and 0.67. 15.The phosphor composition of claim 9, wherein y is between about 0.013and 0.017.
 16. The phosphor composition of claim 9 that absorbsfrequencies of between about 430 and 480 nanometers and emits peakfrequencies of between about 530 and 750 nanometers.